The present invention concerns a method as defined in the preamble of claim 1 and an apparatus as defined in the preamble of claim 11, i.e. a method and an apparatus for providing control parameters to or within a control system.
Control systems generally comprise a control unit typically but not necessarily comprising a central processing unit (CPU), at least one controlled element and utilization means which transform CPU signals if and as necessary and apply them to the controlled element. For this purpose, the CPU and the utilization means need to be connected to each other by communication means such as a bus system. Moreover, external data may need to be communicated to the CPU and/or the utilization means on a corresponding way.
As an example, piezoelectric elements may be used as actuators in fuel injection nozzles (in particular in so-called common rail injectors) of an internal combustion engine. In this example, fuel injection is controlled by means of applying voltages to piezoelectric actuators which expand or contract themselves as a function of the voltage applied. Resulting thereof, an injector needle which is connected to the piezoelectric actuators by means of a transfer system is moved up and down and therefore an injection nozzle is opened and closed. However, the movement of the injector needle is principally influenced by changing rail pressures to which the transfer system and the needle are exposed. In order to nevertheless control the movement of the injector needle with high precision respectively to control the corresponding amount of injected fuel with high precision these influences have to be taken into account. Hence, the appearing rail pressures are measured by measuring means and the voltages which are applied to the piezoelectric actuators are modified in a corresponding way. As a result, a feedback system is implemented, in which rail pressures are measured by measuring means, the measured values are communicated to the control unit, corresponding voltages for the piezoelectric actuators are calculated within the control unit and are communicated from the control unit to an utilization unit, for example an activation IC, from which they are applied to the piezoelectric actuators. The use of piezoelectric elements as actuators proves to be advantageous, inter alia, in fuel injection nozzles for internal combustion engines. Reference is made, for example, to EP 0 371 469 B1 and to EP 0 379 182 B1 regarding the usability of piezoelectric elements in fuel injection nozzles.
Piezoelectric elements are capacitative elements which, as already partially alluded to above, contract and expand in accordance with the particular charge state or the voltage occurring therein or applied thereto. In the example of a fuel injection nozzle, expansion and contraction of piezoelectric elements is used to control valves that manipulate the linear strokes of injection needles. The use of piezoelectric elements with double acting, double seat valves to control corresponding injection needles in a fuel injection system is shown in German Patent Applications DE 197 42 073 A1 and DE 197 29 844 A1, which are incorporated herein by reference in their entirety.
Fuel injection systems using piezoelectric actuators are characterized by the fact that, to a first approximation, piezoelectric actuators exhibit a proportional relationship between applied voltage and the linear expansion. In a fuel injection nozzle, for example, implemented as a double acting, double seat valve to control the linear stroke of a needle for fuel injection into a cylinder of an internal combustion engine, the amount of fuel injected into a corresponding cylinder is a function of the time the valve is open, and in the case of the use of a piezoelectric element, the activation voltage applied to the piezoelectric element.
FIG. 6 is a schematic representation of a fuel injection system using a piezoelectric element 2010 as an actuator. Referring to FIG. 6, the piezoelectric element 2010 is electrically energized to expand and contract in response to a given activation voltage. The piezoelectric element 2010 is coupled to a piston 2015. In the expanded state, the piezoelectric element 2010 causes the piston 2015 to protrude into a hydraulic adapter 2020 which contains a hydraulic fluid, for example fuel. As a result of the piezoelectric element""s expansion, a double acting control valve 2025 is hydraulically pushed away from hydraulic adapter 2020 and the valve plug 2035 is extended away from a first closed position 2040. The combination of double acting control valve 2025 and hollow bore 2050 is often referred to as double acting, double seat valve for the reason that when piezoelectric element 2010 is in an unexcited state, the double acting control valve 2025 rests in its first closed position 2040. On the other hand, when the piezoelectric element 2010 is fully extended, it rests in its second closed position 2030. The later position of valve plug 2035 is schematically represented with ghost lines in FIG. 6.
The fuel injection system comprises an injection needle 2070 allowing for injection of fuel from a pressurized fuel supply line 2060 into the cylinder (not shown). When the piezoelectric element 2010 is unexcited or when it is fully extended, the double acting control valve 2025 rests respectively in its first closed position 2040 or in its second closed position 2030. In either case, the hydraulic rail pressure maintains injection needle 2070 at a closed position. Thus, the fuel mixture does not enter into the cylinder (not shown). Conversely, when the piezoelectric element 2010 is excited such that double acting control valve 2025 is in the so-called mid-position with respect to the hollow bore 2050, then there is a pressure drop in the pressurized fuel supply line 2060. This pressure drop results in a pressure differential in the pressurized fuel supply line 2060 between the top and the bottom of the injection needle 2070 so that the injection needle 2070 is lifted allowing for fuel injection into the cylinder (not shown).
In the example considered, as well as in other control systems, there is a need for a fast communication between the individual components of the control system, particularly between the control unit and the utilization unit, in order to perform a feedback which is as close to realtime as possible. However, there is a delay in accordance with the transmission speed of the communication means as well as with the amount of data which is to be transmitted. Even in control systems which do not require a realtime performance relevant delays may occur for the same reasons. Moreover, for several reasons, such as cost cutting or due to limitations by properties of standard components which are used within a control system, it is often required to use relatively slow communication means instead of the fastest available. Hence, while providing control parameters to or within a control system delays have to be taken into account as according to the state of the art.
It is an object of the present invention, to provide an improved method and apparatus for providing control parameters to or within a control system.
This object of the present invention is achieved by the object of method claim 1, i.e. a method for providing control parameters to or within a control system, in which a plurality of control parameters is transmitted to storage means within the control system by transmission means. The transmitted control parameters are stored within the storage means. Selection parameters are transmitted to selection means within the control system by transmission means. Stored control parameters are selected in accordance with transmitted selection parameters by the selection means. Then, the selected parameters are utilized for controlling the system. Furthermore, the object of the present invention is achieved by the object of apparatus claim 11, i.e. an apparatus, in particular eligible for usage with the inventive method, which comprises a control unit and an activation IC connected to each other by transmission means, storage means which are implemented in the activation IC, and selection means which are implemented in the activation IC.
As stated in claims 1 and 11, the general approach of the invention is to predictively provide a plurality of control parameters in advance and then to further provide selection parameters within a control system. Hence, the amount of control data which are transmitted between the individual components of the control system is increased. However, recalling, that it is an object of the invention to avoid disadvantages due to transmission delays, one would expect that it is therefore necessary to reduce the amount of control data which are transmitted to the minimum. Therefore, the approach of the invention, namely increasing instead of reducing the amount of transmitted control data, is just the opposite of what one would expect to be an eligible approach. Beyond this background, the surprising effect of the invention is that by means of the inventive approach the performance of the control system is improved.
Preferably, the control system comprises a control unit and an activation IC. The control parameters are transmitted within the control system from the control unit to storage means within the activation IC. And the selection parameters are transmitted within the control system from the control unit to a logic circuit within the activation IC (claim 2).
In principle, the inventive method could also be used with storage means and selection means which are implemented independently from each other. However, the advantages of the inventive method may be increased by utilizing storage means and a logic circuit which are both implemented within a single IC.
As according to claim 3, the control parameters are transmitted by means of a serial bus.
In principle, one would expect that a reduction of transmission times for control data would require the preferred use of high speed transmission means such as parallel bus systems. However, according to the invention there is no need to transmit the control parameters by such fast transmission means. Hence, the usage of a serial bus system is sufficient and advantageous since it allows to reduce the costs of the control system.
As stated in claim 4, the selection parameters are preferably transmitted by means of a parallel bus.
Preferably, system parameters are measured by measuring means and control parameters are determined in accordance with measured system parameters by determination means within a control unit (claim 5).
This allows to take into account a current status of the control system within the control parameters.
As according to claim 6, preferably system parameters are measured by measuring means and selection parameters are determined in accordance with measured system parameters by determination means within a control unit.
This allows to perform a feedback system, which is in particular but not necessarily advantageous in combination with the method as according to claim 5.
In a preferred implementation of the inventive method, firstly, a plurality of control parameters is transmitted from a control unit by a serial bus system to storage means within an activation IC and stored in said storage means. Secondly, system parameters are measured by measuring means. Thirdly, selection parameters are determined in accordance with measured system parameters by determination means within the control unit. Fourthly, selection parameters are transmitted by a parallel bus system from the control unit to logic means within the activation IC. And fifthly, selection parameters are utilized for the selection of one or more particular of the stored control parameters by the logic means within the activation IC (claim 7).
This results in a particularly advantageous combination of the various before mentioned modifications of the inventive method.
Preferably, the plurality of control parameters comprises one or more base parameters which are corresponding to general and/or measured system parameters. The plurality of control parameters comprises one or more offset parameters which are corresponding to general and/or measured system parameters. The selection parameters cause logic means to either only select base parameters or to select base parameters and offset parameters. And in case of a selection of base parameters and offset parameters the selection parameters further cause the logic means to add the offset parameters to the base parameters by addition means within the activation IC).
This allows to apply the same corrections due to one (or more) system parameters to several different elements within the control system which require different control parameters by means of adding corrective offsets to the different base control parameters as required.
Advantageously, the selected and/or added control parameters correspond to values of target voltages. Moreover, the selected and/or added control parameters are converted into their corresponding voltages by means of digital to analog converters. And the voltages obtained are transported to elements within the controlled system by transportation means.
Within a correspondingly controlled system the advantages of the inventive method can be particularly scooped.
Preferably, the voltage receiving elements within the controlled system are piezoelectric elements and the applied voltages correspond to any desired extension of the piezoelectric elements. The advantage is that the voltage is very well-adjusted to the actual operating point.
Within a preferred embodiment of the inventive apparatus, there are first transmission means between the control unit and the activation IC implemented as a serial bus system and second transmission means between the control unit and the activation IC implemented as parallel bus system (claim 12).
This results in an inexpensive and fast control system as utilized according to the inventive method.
The invention will be explained below in more detail with reference to exemplary embodiments, referring to the figures.